The present invention relates generally to manually controlled parking brakes for rail vehicles and more specifically to a manual parking brake for locomotives and car mounted cylinders for rail cars.
Current locomotive parking brake systems require high manual input force to apply an unknown brake shoe force through a complex system of levers, chains and brackets. The high manual force could result in injuries to the operator as well as applying an unknown parking brake force on the wheel.
Typically, the hand brake or parking brake consists of a device for manually applying a brake shoe to the wheel of a railroad car by turning a hand wheel or pumping a handle connected by gears and/or linkages to the brake shoe. This linkage is the same linkage which is used to apply or release the brakes throughout the train. Typical examples are shown in U.S. Pat. Nos. 4,746,171 and 5,701,974. The manual apply and release forces are required because the car or locomotive does not include a source of air pressure, which is normally used to control the brakes, in the park or isolated position. An example of the hydraulic brakes with a reservoir pump and pump actuated means is shown specifically in U.S. Pat. No. 5,701,975.
Although the brake systems of various types have been applied to rail cars, there is a need for a locomotive manual parking brake which is capable of applying a substantially greater known braking force. If such a brake is available, the brake on less than all of the wheels of the locomotive can be applied in park to maintain the locomotive in a brake condition.
The parking brake of the present invention includes an electric motor controlling a hydraulic pump fluidly connected to and controlling a bidirectional hydraulic actuator for the wheel brakes. An electrical controller is connected to the pump and controls activation/deactivation and direction of activation of the pump. The controller may include a bidirectional electric motor coupled to a bidirectional pump and a selection switch which selectively connects the electrical motor to an electrical source in opposite polarities. The selection switch also selectively disconnects the electric motor from the electrical source. Alternatively, a unidirectional electric motor and unidirectional pump are connected to the actuator by a selection valve to the actuator.
The controller can also include a pressure switch response to fluid pressure between the pump and the hydraulic motor and the controller deactivates the pump for excessive pressure. A pressure relief valve for the fluid pressure between the pump and the hydraulic motor may also be provided. Preferably, the pump is connected to the hydraulic motor by a pair of passages and the controller includes a pair of pressure switches and relief valves, each responsive to pressure in a respective passage.
The controller may also include a limit switch responsive to the position of the actuator and the controller deactivates the motor and the pump when the actuator element reaches a predetermined position. The brake system includes a hydraulic reservoir. The controller includes a level switch responsive to the level of fluid in the reservoir and the controller deactivates the motor and the pump for a low level of hydraulic fluid in the reservoir.
The controller may activate the pump in one direction of activation if both the pressure and the limit switches are closed. The pump is also activated in the other direction of activation if the pressure switch is closed, even if the limit switch is open. The actuator element may include a coupler for coupling to either the brake bream of the wheel brakes or the actuator or brake cylinder system of the wheel brakes.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.